Conventionally known is a robot of a type in which the pose (position and posture) of a tool attached to a robot hand is controlled for required operation. For example, an articulated robot is known which comprises an arm consisting of a series of links connected to one another for relative rotation and a hand connected to the distal end of the arms so that the hand and hence the tool can assume any desired postures within a three-dimensional space. The robot is previously instructed for the positions of a starting point and an ending point of operation and postures of the tool at the starting and ending points. In operation, interpolation is executed on the basis of these instruction data, whereby the pose of the tool is controlled from the starting point to the ending point.
In linearly moving the tool from the starting point toward the ending point, for example, the robot calculates two parameters .alpha.1 and .alpha.2 shown in FIG. 5, in accordance with the instruction postures at the starting and ending points. In FIG. 5, symbols VI and V2 designate approach vectors indicative of the directions of the tool at the starting point P1 and the ending point P2, respectively, and symbol V1' designates a vector obtained by moving the vector V1 in parallel relation such that the starting point of the vector V1 coincides with the ending point P2. The parameter .alpha.1 represents an angle (variation of the tool direction from the starting point to the ending point) formed between the vectors V1' and V2 within the plane which contains these two vectors, while the parameter .alpha.2 represents the variation of the rotational position of the tool around the axis thereof, between the starting and ending points. The robot linearly interpolates these parameters .alpha.1 and .alpha.2 between the starting and ending points P1 and P2, thereby controlling the posture of the tool. It is difficult, however, to control the tool posture as intended by this method.
Further, in moving the tool from the starting point P1 to the ending point P2 along a circular arc 2, as shown in FIG. 6, the robot is instructed for the respective positions of the starting and ending points and an intermediate point P3 and the postures of the tool at the starting and ending points. During the operation, the tool position is controlled so that the path of transfer of the tool coincides with the circular arc 2, and the tool posture is controlled by the method described with reference to FIG. 5. Thus, in moving the tool along a circular arc, especially a major arc, the tool posture control is more difficult than in linearly moving the tool.